The native fish that inhabit the freshwater system of Puerto Rico are amphidromous (part of their lifes occur in the river and part on the ocean) or catadromus (migrate from the stream to the ocean to reproduce). These species utilize upper and lower reaches of the streams, but some of them have the adaptation to migrate through the vertical wall of the water falls. In general the lower reaches are dominated by mountain mullet (Agnostomos monticula), big mouth sleeper (Gobiomorus dormitor), smallscaled spinycheek sleeper (Eleotris perniger), omnivorous goby (Awaous taiasica), and the American eels (Anguilla rostrata); while the upper parts of the streams are inhabited by river gobies (Sicydium plumieri). Sicydium and Awaous have modified pectoral fins that use to climb the waterfalls.
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